Chemical Equations & Reactions (Rxns) Chapter 8 Chemical Equations & Reactions (Rxns)

Chemical Reactions (Rxns) Chemical Reaction: the process in which one or more substances is changed into one or more different substances Chemical Equation: Reactants  Products Chemical equations use symbols & formulas to identify the amount and type of chemical reactants & products in a reaction Ex: C6H12O6(s) + 6O2(g)  6 H2O(l) + 6 CO2(g) State of Compound # of Molecules

Characteristics of Chemical Reactions 1) A chemical equation must represent all reactants and products 2) A chemical equation must contain correct formulas for reactants and products 3) Conservation of mass must be expressed in the equation

Indicators of Chemical Reactions Evolution (emitting) of light and heat Production of gas (bubbling) Formation of a Precipitate (liquid + liquid  solid) Color change

Significance of Chemical Reactions Coefficients indicate relative amounts of reactants and products Ex: H2 + Cl2  2HCl * Coefficients indicate mole ratio 1 Mole 1 Mole 2 Moles

Symbols Used in Chemical Reactions

More Symbols

Types of Equations Word Equations- use molecular names of reactants and products Ex: methane gas + oxygen gas yields carbon dioxide gas and liquid water Formula Equations- use chemical formulas to represent reactants and products Ex: CH4(g) + 2O2(g)  CO2(g) + 2H2O(l)

Balancing Equations A balanced equation has an equal # of all atoms on both sides of the chemical equation Ex. __ Mg + __ Cl  __ MgCl2

Balancing Equations Balance each type of atom one at a time. Balance atoms that appear once on each side first. Treat polyatomic ions as one entity. Balance hydrogen & oxygen atoms last. Count your atoms to be sure the equation is balanced. If the coefficients have a GCF, divide!

Balancing Equations – Practice! Ex: __C2H4 + __O2  __CO2 + __H2O __ Na3PO4 + __ KOH __ NaOH + __ K3PO4

Types of Chemical Reactions Synthesis Reaction: 2 or more substances combine to form 1 new compound (A + X  AX) Ex: 2Mg(s) + O2(g)  2MgO(s) Decomposition Reaction: 1 substance breaks down into 2 new substances (AX  A + X) Ex: CaCO3(s)  CaO(s) + CO2(g)

Reaction Types Single-Replacement Reaction: one element replaces a similar element in a compound (A + BX  AX + B) Ex: 2Al + 3Pb(NO3)2  3Pb + 2Al(NO3)3 Double-Replacement Reaction: ions of 2 compounds exchange places in an aqueous solution (AX + BY  AY + BX) Ex: 2KI + Pb(NO3)2  PbI2 + 2KNO3

Reaction Types Combustion Reaction- a fuel (hydrocarbon) combined with oxygen produces carbon dioxide and water Ex: C3H8 + 5 O2  3 CO2 + 4 H2O Fuel Oxygen Carbon Dioxide Water

Determining Reaction Types

Activity Series of Elements The activity series is a list of elements organized according to the ease with which the elements undergo certain single-replacement reactions Listing shows elements from most active to least active Used to predict whether a reaction will or will not occur

Activity Series

Activity Series Examples Ex: __ Al + __ ZnCl2  __ Co + __NaCl 

END OF CHAPTER 8 NOTES!!!